/****************************************************
 * The SNIFFER Checksums Library
 * -----------------------------
 *
 * C. Nunez 	(cnunez@stevens.edu)
 * W. Best		(wbest@stevens.edu)
 * K. Fuhrman 	(ktfuhrman@gmail.com)
 * M. DiAmore 	(mdiamore@gmail.com)
 *
 * Date Created:	15 April, 2010
 *
 * Description
 * -----------
 * These are checksum calculation methods for various
 * protocols supported by SNIFFER.
 *
 ****************************************************/

#include "sniffer_checksums.hpp"

/*******************************************************************
 * u_short ipv4_ cksum (struct ip *i, int len)
 * -------------------------------------
 *
 * Description: Calculates IP checksum.
 *
 * Returns: 	u_short sum.
 * Requires: 	struct ip *i,
 * 				int len
 *
 * Copyright notice:
 * -----------------
 *
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
 *     The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary form, with or without
 * modifications, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ''AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *******************************************************************/

u_short ipv4_cksum(struct ip *ip, int len)
{
	
	long sum = 0;  /* assume 32 bit long, 16 bit short */
	
	while(len > 1){
		sum += *(unsigned short*) ip++;
		if(sum & 0x80000000)   /* if high order bit set, fold */
			sum = (sum & 0xFFFF) + (sum >> 16);
		len -= 2;
	}
	
	if(len)       /* take care of left over byte */
		sum += (unsigned short) *(unsigned char *)ip;
	
	while(sum>>16)
		sum = (sum & 0xFFFF) + (sum >> 16);
	
	return ~sum;
}